Supersonic compression represents game-changing technology

Using aerodynamic design principles common in flight and propulsion-based systems, the Dresser-Rand business’ supersonic technology has game-changing implications for ground-based compressor applications.

The Dresser-Rand business has been a global leader in designing and developing rotating equipment and compression technology for more than 100 years. In 2014, the company took steps to further its position as a technology leader within the industry with the acquisition of key assets from Ramgen Power Systems, LLC.

The acquisition came at the end of a six-year period, during which Dresser-Rand, in partnership with the U.S. Department of Energy, leveraged its resources and expertise to accelerate the development of supersonic compression technology.

Factory testing on a 2,200 PSIA (152 bara) discharge pressure supersonic compressor (using CO2 gas) recently concluded at the Dresser-Rand business facility in Olean, NY. During the tests, the compressor consistently achieved 10:1 compression ratios with discharge temperatures of 550°F (288°C) using a single impeller. The technology is now in the commercialization phase and has game-changing implications for a number of market applications.

Supersonic Compression Technology Overview
The Dresser-Rand business and the U.S. Department of Energy co-funded development of supersonic compression with the primary goal of improving efficiency and reducing capital and operating costs for carbon capture and sequestration (CCS) applications. Carbon dioxide is a medium molecular weight gas that requires “100:1” total compression ratio (i.e. fossil fuel-fired power plants).

The technology can also be used in low molecular weight compression applications, such as air separation and most upstream and downstream refining applications. It’s also ideally suited for enhanced oil recovery (EOR) techniques that employ CO2 injection.

Supersonic compression applies aerodynamic design practices to ground-based compressors. Impellers are rotated to high peripheral speeds to create a shockwave in the stationary diffuser at the tip of the impeller (above Mach 1).

Traditionally, it was common practice for compressor designers to limit impeller speed in order to prevent formation of a shockwave and subsequent disruption of gas flow. However, through extensive research and development, the Dresser-Rand business, together with Ramgen, developed a design that harnesses the shockwave to aid in compression.

The generation of a shockwave in the diffuser results in a rapid increase in the density of the gas. It is a key differentiator in the technology that allows a single-stage supersonic compressor stage to achieve up to five times higher pressure ratios than traditional subsonic compression stages.

Operational Advantages
Supersonic compression technology represents a significant advancement in the state-of-the-art for many compressor applications. Its primary competitive advantage is that it can achieve high compression efficiency at high single-stagecompression ratios, which allows operators to increase the power density of machinery and take advantage of waste heat.

In traditional compression systems, a portion of the total energy input is lost as low-grade heat. In a compressor using supersonic technology, more aerodynamic work is being done in a smaller area and these losses are manifested as mid-grade heat. As a result, operators can harvest waste energy streams to reduce power consumption. This is particularly advantageous in high molecular weight compression projects that are footprint-constrained or in facilities that have the necessary systems to use waste heat for such things as boiler feed water preheating, sorbent drying, coal drying, or amine solution regeneration. In these instances, a supersonic compressor will have lower net power consumption.

Another benefit that comes as a result of waste heat integration is reduced water consumption. Supersonic compression technology requires considerably less water for cooling because heat of compression can be transferred directly into the process via a heat exchanger. The residual low temperature waste heat that cannot be used in the process is then sent to a gas cooler. This is in contrast to traditional compression units, where all the heat of compression is absorbed by water in a gas cooler and then evaporated into the atmosphere. In some cases, the amount of water used for cooling can be substantial.

For example, a large integrally geared unit may require more than 8,000 gallons per minute of cooling water. A supersonic compressor that first transfers much of its heat to the process needs only 900 gallons per minute, representing a more than 80% decrease.

Looking Ahead
Supersonic compressors enable operators to achieve substantially higher single-stage compression ratios (up to 10:1) than comparable subsonic units on the market today. The Dresser-Rand business continues to develop and commercialize this technology to reduce capital and operating costs, improve efficiency and minimize the footprint of compression for both high and low molecular weight applications, including CCS, EOR using CO2 injection and air separation.

Conceptual design of a higher flow, low-pressure (LP) compressor has been completed by the Dresser-Rand business and is on schedule to meet target dates for testing and program completion in early 2018. Lessons learned from 2,200 PSIA (152 bara) discharge pressure, lower flow compressor tests are being incorporated in the design of the LP unit. Support from the U.S. Department of Energy, along with access to the agency’s Oak Ridge Leadership Computing Facility (OLCF) Titan supercomputer has played a key role in optimizing the aerodynamic design of the compressors and bringing this game-changing technology to market.

With 2,200 PSIA (152 bara) discharge pressure, low flow testing complete, the Dresser-Rand business is now in the process of identifying opportunities to pilot test supersonic compression technology in field applications.

Tags: CCS, EOR, Ramgen Power Systems

other articles from insights issue 06.2017